Actuator system for a controlled coolant pump

ABSTRACT

A coolant pump of an internal combustion engine, with a pump housing and a hollow shaft rotatably mounted therein. Coolant is delivered via an impeller wheel from a suction connection. The flow is controlled by a guide plate on the impeller wheel that is variably displaceable axially between two end positions. The guide plate is adjustable by a push rod actuator guided in the pump shaft. The actuator has a radial piston pump integrated within the coolant pump with an intake piston and a counterpiston guided in the pump shaft, that are inserted lying opposite one another and delimit a pressure space. The pistons are enclosed outside by a linearly displaceable control element guided in the pump housing. Adjustment of the control element takes place as a function of a rotary angle of the pump shaft via an actuator unit having an electrically operated actuating element and a linear freewheel.

INCORPORATION BY REFERENCE

The following documents are incorporated herein by reference as if fully set forth: German Patent Application No.: 102012208103.8, filed May 15, 2012.

BACKGROUND

The invention relates to a controlled coolant pump for an internal combustion engine.

In the case of liquid-cooled, in particular water-cooled internal combustion engines, the cooling water is guided in a closed circuit through cooling channels of the crankcase and of the cylinder head and is subsequently cooled again in an air/water heat exchanger or radiator. A coolant pump which is, in particular, driven directly via a belt drive is used to assist the circulation of the coolant. A dependence of the pump rotational speed on the rotational speed of the internal combustion engine is produced as a result of the direct coupling between the coolant pump and the crankshaft. It follows from this that, in the case of a cold start of the internal combustion engine, the coolant circulates, as a result of which desired rapid warming of the internal combustion engine and an associated optimum operating temperature are delayed. For the optimization of internal combustion engines with regard to emissions and fuel consumption, it is appropriate to bring the internal combustion engine to the operating temperature as quickly as possible after the cold start. As a result, both the frictional losses and, as a result, the fuel consumption and at the same time the emissions values are reduced. In order to achieve this effect, controllable coolant pumps are used, the delivered volumetric flow of which can be adapted to the cooling requirement of the internal combustion engine. For internal combustion engines which are intended for vehicles, a coolant flow of <0.1 1/h, which is also called a “zero leakage flow”, is also aimed for in the cold running phase.

DE 199 01 123 A1 has disclosed, as a measure to influence the delivery volume of a coolant pump, assigning to the impeller wheel an outer slide which engages over it. In this way, the effective impeller width of the impeller wheel can be changed and set in the axial direction in an infinitely variable manner. Here, the adjustment of the slide takes place by way of the rotation of a thread-like guide. DE 10 2005 062 200 A1 discloses a controllable coolant pump, in which a valve slide which can be displaced in the direction of the pump shaft axis is introduced within the pump housing in order to influence the delivery quantity. The slide of annular configuration forms an outer cylinder which covers the outflow region of the impeller wheel in a variable manner. According to DE 10 2005 004 315 A1, the valve slide, which can also be called a guide disk, is adjusted electromagnetically by way of a magnet coil which is arranged in the pump housing. As an alternative to this, a pneumatically or hydraulically operated actuator, which includes push rods which are guided in the pump housing in order to adjust the valve slide, is provided for the adjustment of the valve slide according to DE 10 2005 062 200 A1.

SUMMARY

It is the object of the present invention to provide an actuator system for a controllable coolant pump, which actuator system is optimized in terms of installation space and costs, is functionally reliable and ensures an adjustment of the guide plate, which adjustment is tailored to requirements.

This objective is met by a controllable coolant pump having one or more features of the invention. Advantageous refinements are specified below and in the claims.

According to the invention, the actuator system which is integrated within the coolant pump affords the advantage of reducing the installation space and the production costs for realizing an effective and functionally reliable controllable coolant pump. For the generation of pressure, the construction according to the invention comprises an actuator system having a radial piston pump which is integrated within the coolant pump and includes two pistons, a main piston and a counterpiston, which are guided in a through hole of the pump shaft and are inserted so as to lie opposite one another. The pistons which delimit a pressure space are enclosed on the outside by a control element which forms an eccentric, also called a slide and by way of which an oscillating movement of the pistons can be triggered. A change in the volumetric flow of the coolant pump via a guide plate displacement is triggered by an adjustment of the control element in the direction of a greater eccentricity. The radially or linearly displaceable control element which is guided in a cutout in the pump housing can be set via an actuator unit as a function of a rotary angle of the pump shaft, which actuator unit includes an electrically operated actuating element and a linear freewheel. The required actuating force for adjusting the control element is generated by the electric actuating element, it being possible for the required actuating force to be reduced according to the invention by the linear freewheel. In conjunction with the linear freewheel, an adjustment of the control element can advantageously be limited to rotary angle phases of the water pump shaft, in which rotary angle phases a reduced pressure is set in the pressure space of the radial piston pump. In the case of a pressure rise, the adjustment is blocked temporarily by the linear freewheel until a next rotary angle phase with reduced pressure is reached. Consequently the control element can be adjusted with a relatively low actuating force level of the actuator unit.

Due to the cyclical adjustment of the control element which is carried out exclusively with reduced actuating forces, a small and inexpensive electrical actuating element which is optimized in terms of installation space can advantageously be used. Resetting of the guide plate into an initial or neutral position in order to achieve a large volumetric flow takes place automatically in the case of a powerless actuating element as a result of centrifugal forces which act on the linear freewheel and/or by an assisting spring force. By use of the radial piston pump, the cooling medium is sucked in from the cooling circuit or the coolant pump and is transferred to a pressure space which lies in the coolant pump shaft. A control pressure can be generated by way of the radial piston pump in conjunction with a variable eccentricity, in order to adjust the piston between zero or idling operation and a variable stroke. Furthermore, the speed of the pressure build-up and therefore the position of the guide plate with respect to the impeller wheel can be controlled in an infinitely variable manner, in order to achieve rapid warming of the internal combustion engine after a cold start or to influence the engine temperature in a targeted manner. In comparison with previous, for example electric-motor, complex and expensive embodiments for realizing a controllable coolant pump, the invention advantageously provides a concept which is neutral in terms of installation space, easy to assemble and inexpensive. Furthermore, the construction which is easy to assemble of the actuator system according to the invention does not impair the installation space in the region of the drive or belt plane of the coolant pump. The actuator system can therefore be realized within the packaging limits of a conventional coolant pump, formed of pulley wheel, mounting, slide ring seal and impeller wheel. Moreover, the concept according to the invention which ensures a satisfactory actuating capability of the guide plate and satisfies all the criteria from the client viewpoint can be realized with standardized components.

According to one preferred refinement of the invention, the linear freewheel of the actuator unit comprises at least two clamping bodies which make a self-locking action possible depending on defined variables and form a clamped assembly. To this end, the clamping bodies are inserted in a guide sleeve and are guided on the outside on the cutout of the pump shaft and on the inside on a clamping cone. Furthermore, the clamping cone which tapers in the direction of the guide sleeve and is connected to the control element is enclosed by a compression spring which is inserted between the control element and the guide sleeve. In the case of a powerless actuating element or in the case of a relatively low actuating force of the actuating element, the axial force of the compression spring releases the clamping bodies and therefore the clamped assembly and displaces the guide sleeve and the actuating element into an initial or neutral position. An electromagnet, the actuating force of which adjusts the linear freewheel, the control element which is connected thereto, and the associated pistons, is suitable, in particular, as electrical actuating element. On account of the adjustment according to the invention which is limited to rotary angle phases of the water pump shaft and interacts with the linear freewheel, an electromagnet can advantageously be used which is inexpensive and is optimized in terms of installation space.

Furthermore, according to the invention, a design is advantageously provided for the actuator unit, which design provides a range of force of ≧10 N for the electrical actuating element and a range of force of from ≧1.2 N to ≦3 N for the compression spring which is inserted between the linear freewheel and the actuating element. In order to achieve a self-locking action, the clamping cone of the linear freewheel has a wedge angle α of ≦5.7°, a coefficient of friction μ of 0.1 being taken into consideration.

As a measure for ensuring the functional reliability of the actuator system, the control element, which can be displaced radially in an infinitely variable manner and influences the eccentricity and therefore the stroke of the pistons of the radial piston pump, is inserted in the pump housing such that it is sealed. The pistons, the main piston and the counterpiston, which are offset by 180° with respect to one another are guided on the inner contour of the control element which is still rotationally fixed, such that they are mounted on sliding bearings or antifriction bearings. A spring element which is inserted between the pistons brings about an assisting nonpositive support of the pistons on the control element. The main piston which is configured as a hollow body includes an intake valve which interacts with an intake or inflow channel of the pump housing, via which the hydraulic fluid or coolant of the coolant pump enters into the main piston in an intake phase. Moreover, a nonreturn or one-way valve is integrated into the main piston, via which valve the hydraulic fluid flows into the pressure space of the pump shaft, which pressure space is delimited by the main piston and the counterpiston. A further one-way valve, which is also called a closing valve, is provided between the pressure space and an inflow channel of a high pressure space of the pump shaft, in which high pressure space an actuating or working piston, which loads the push rod of the guide plate, is guided displaceably.

A defined leakage gap between the working piston and the bore wall of the pump shaft ensures automatic escape of hydraulic fluid out of the high pressure space into the coolant pump. This takes place as soon as the electrical actuating element of the actuator unit is switched to the powerless state, and the working piston and at the same time the guide plate which is connected thereto are displaced in the direction of an end position, as a result of which the volumetric flow of the coolant pump is increased.

Furthermore, it is possible according to the invention to combine the actuator system with a failure safeguard or failsafe device. To this end, the push rod is assigned a spring element, in particular a compression spring, which, in the case of a disruption, for example a power failure of the actuator unit, displaces the push rod including the associated guide plate into the neutral position, in which the maximum delivery or volumetric flow of the coolant pump is set.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following text the invention will be explained using preferred embodiments with reference to the appended figures, in which:

FIG. 1 shows a diagrammatic illustration of the construction of a coolant pump having an integrated actuator system which is constructed according to the invention,

FIG. 2 shows a coolant pump according to the invention in a longitudinal section,

FIG. 3 shows a functional principle diagram of the radial piston pump of the actuator system,

FIG. 4 shows a diagram of the force profile for adjusting the control element of the radial piston pump, and

FIG. 5 shows a diagrammatic illustration of the clamped assembly of the linear freewheel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 diagrammatically shows all the components of a coolant pump 1 which is controlled according to the invention. The coolant pump 1 which is intended to cool an internal combustion engine 2 is driven via a traction mechanism drive 3. The traction mechanism 4 of the traction mechanism drive 3 which is configured as a belt drive connects a first pulley wheel 5 which is connected to a crankshaft (not shown) of the internal combustion engine 2 to a second pulley wheel 6 which is assigned to the coolant pump 1. The delivery volume or the volumetric flow of the coolant pump 1 which is connected to a cooling circuit 7 can be set or controlled via a hydraulically active actuator system 10 which is assigned to a hydraulic circuit 8 and is integrated into the coolant pump 1. The construction of the actuator system 10 comprises an eccentrically adjustable radial piston pump 11 which interacts with an actuator unit 15 which includes a linear freewheel 12 and an actuable actuating element 13.

FIG. 2 shows the controllable coolant pump 1 in longitudinal section and clarifies, in particular, the construction of the actuator system 10. The coolant pump 1 comprises a pump housing 18, in which a pump shaft 20 is mounted rotatably via an antifriction bearing 21, which pump shaft 20 is configured as a hollow shaft and is connected in a rotationally rigid manner to an impeller wheel 19. In the operating state of the coolant pump 1 in the case of a rotating impeller wheel 19, the coolant flows as hydraulic fluid axially via a suction connection 22 to the impeller wheel 19 and is guided radially into a spiral channel 23 or pressure channel. Here, a pump cover 24, which is connected to the impeller wheel 19, forms a transition between the suction connection 22 and the spiral channel 23. In order to influence the volumetric flow of the coolant pump 1, a guide plate 25 which axially displaceably covers the outflow region 26 in a variable manner is assigned to the impeller wheel 19 in the outflow region 26 of the coolant pump 1. To this end, the guide plate 25 is connected in a rotationally fixed manner to a push rod 18 which can be displaced axially in the pump shaft 20. Via the actuator system 10, the push rod 28 and, as a result, the guide plate 25 can be positioned in an infinitely variable manner between two end positions which are defined by the pump cover 24 and a rear wall 27 of the impeller wheel 19. According to the position of the guide plate 25 which is depicted in FIG. 2 and is supported on the rear wall 27, a maximum volumetric flow of the coolant pump 1 is set. The eccentrically adjustable positive displacement pump of the actuator system 10, which positive displacement pump is configured as a radial piston pump 11, includes two pistons, a main piston 29 and a counterpiston 30, which lie opposite one another and are guided in a radial through hole 31 of the pump shaft 20. On the outside, the pistons 29, 30 are enclosed by a control element 32 which can also be called a slide and are supported nonpositively with a rounded piston tip which is designed convexly or as a spherical cap on an inner contour 33 of the control element 32 in the operating state in a manner which is induced by centrifugal force and is assisted by a spring element 37 which is inserted between the pistons 29, 30. The pistons 29, 30 can be displaced radially in the pump housing 18 via the control element 32 in order to set an eccentricity E between a rotational axis 35 of the coolant pump 1 and a rotational axis 36 of the control element 32. To this end, the control element 32 is inserted in a cutout 34 of the pump housing 18 such that it can be displaced radially or linearly and in a sealing manner by a seal 38, and makes an eccentric adjustment of the main piston 29 and of the counterpiston 30 possible. In order to reduce the friction and therefore the wear, contact faces of the pistons 29, 30 and the inner contour 33 of the control element 32 are hardened locally or are coated, for example, with Teflon or molybdenum and/or with a lubricant. As an alternative to a sliding mounting, an antifriction mounting can be provided, in which the pistons 29, 30 are enclosed by an intermediate ring which encloses on the outside and includes a circumferential raceway for rolling bodies, which raceway corresponds with a further inside raceway of the control element 32, which raceway is of complementary design.

The eccentricity E and, as a result, a stroke of the oscillating pistons 29, 30 of the radial piston pump 1 can be set directly via the actuator unit 15 of the actuator system 10. From the, in particular, electrically operable actuating element 13 of the actuator unit 15, an actuating force can be transmitted in the arrow direction to a linear freewheel 12 and from there to the control element 32. Here, the actuating element 13 is assigned a guide sleeve 41 which is of cup-like design and is connected to the linear freewheel 12. The linear freewheel 12 forms a clamped assembly 39, which makes a self-locking action possible, with two clamping bodies 40 which are positioned so as to lie opposite one another and are inserted into local openings of the guide sleeve 41 of cup-like design. On the outer side, the clamping bodies 40 are guided on the cutout 34 of the pump housing 18 and, on the inner side, the clamping bodies 40 enclose a clamping cone 42 which tapers in the direction of the guide sleeve 41 and is connected to the control element 32. A cyclical adjustment of the control element 32 with a relatively low actuating force, which adjustment is limited to the intake phase of the main piston 29 of the radial piston pump 11, can be realized by means of the actuator unit 15. The actuating force which is exerted by the actuating element 13 is transmitted to the guide sleeve 41, on account of direct support, and from there directly to the control element 32. After the end of the intake phase and the reaching of an increased pressure level within the pressure space 49 which is delimited by the pistons 29, 30, the position of the control element 32 is held by the linear freewheel 12 which locks in the arrow counterdirection. In the case of a deactivated, powerless actuating element 13, the clamped assembly 39 of the linear freewheel 12 is released, by a compression spring 43, which encloses the clamping cone 42 and is positioned between the control element 32 and the guide sleeve 41, exerting an axial force which releases the clamping bodies 40. Synchronously with this, the guide sleeve 41 and, as a result, the control element 32 are displaced in the direction of a neutral or initial position without eccentricity.

In the region of great eccentricity E, coolant flows as hydraulic fluid via an intake valve 46 of the main piston 29 into a piston interior space. A push-out opening 47 of the main piston 29 is assigned a one-way valve 48, via which the hydraulic fluid flows into the pressure space 49 of the radial piston pump 11 in a pumping phase of the radial piston pump 11. The intake valve 46 is preferably connected to the spiral channel 23 or a pressure region of the coolant pump 1, as a result of which the prevailing back pressure assists the opening of the intake valve 46 at the beginning of the intake phase of the main piston 29. The further counterpiston 30 is provided for mass compensation or for radial mass distribution with respect to the intake piston 29. In the pumping phases which end at a rotary angle of 180° and 360° and follow the intake phases of the radial piston pump 11, the pressure in the pressure space 49 is boosted to a maximum. Via a closing valve 51 which likewise acts as a one-way valve and is inserted in a longitudinal bore 50 of the pump shaft 20, the hydraulic fluid is displaced out of the pressure space 49 into a high pressure space 52 of the pump shaft 20 during the actuation in the pumping phase. Here, an actuating piston 54 which is guided displaceably in the high pressure space 52 and is connected indirectly via the push rod 28 to the guide plate 25 is pressure-loaded. The closing valve 51 opens as soon as a pressure gradient is set and the pressure in the pressure space 49 exceeds the pressure level in the high pressure space 52. An actuating movement of the push rod 28 and of the guide plate 25 which is connected to it in the direction of the pump cover 24 is triggered via the actuating piston 54 when the pressure in the high pressure space 52 exceeds the spring force of a compression spring which can also be called a failsafe device 56. The compression spring which counteracts the actuating movement of the actuating piston 54 is supported between a shoulder of the pump shaft 20 and the actuating piston 54 and encloses the push rod 28 here. As a measure for counteracting an uncontrolled pressure rise in the high pressure space 52, a pressure relief valve can be integrated, for example, into the pump shaft 20, which pressure relief valve opens when a limit pressure is exceeded and makes an outflow of coolant out of the high pressure space 52 possible. In order to ensure rapid restoring of the guide plate 25, it is possible, furthermore, to introduce a defined leakage gap, for example in the form of a longitudinal channel, in the outer contour of the actuating piston 54, via which leakage gap coolant is discharged out of the high pressure space 52 into an annular space which is intended for the compression spring of the failsafe device 56 and from there via an outflow opening of the pump shaft 20.

FIG. 3 shows a functional diagram of the radial piston pump 11 and FIG. 4 shows a diagram of the force profile which is generated by the radial piston pump 11. As clarified by FIG. 3, one revolution of the main piston 29 results in two intake operations and two pumping operations, the phases of said operations differing as a result of the eccentricity E which is set between the rotational axis 35 of the pump shaft and the rotational axis 36 of the radial piston pump 11. A short intake phase is set between 0° and 90° and a short pumping phase is set between 90° and 180°. Deviating from this, an extended intake phase results between 180° and 270° and an extended pumping phase results between 270° and 360°. The diagram according to FIG. 4 graphically shows the force profile of the radial piston pump 11 in relation to the rotary angle of the radial piston pump 11, the rotary angle of the radial piston pump 11 being plotted on the abscissa and the force N being plotted on the ordinate. As can be gathered from FIG. 4, a relatively low force level is set in the intake phases between 0° and 90° and between 180° and 270°, which relatively low force level is used according to the invention to adjust the control element 32 via the actuator unit 15.

FIG. 5 diagrammatically shows the clamped assembly 39 of the actuator unit 15 and the forces which act for the clamping action. In the pumping phases of the radial piston pump 11, a locking function of the clamped assembly 39 is set, in which locking function the clamping bodies 40 are supported nonpositively on the outer side on the cutout 34 of the pump housing 18 and on the inner side on the clamping cone 42 of the control element 32. In the intake phases of the radial piston pump 11, the clamped assembly 39 is released from the actuating unit 13 of the actuator unit 15 by the spring force F_(fed) of the compression spring 43.

The following relations apply to the clamped assembly 39 of the linear freewheel 12:

N−Fe _(exz)/tan(α)=0; R−F _(fed) −F _(exz)=0; N=R/μ

In the case of the following assumptions: μ=0.1; α=5°; F_(exz) =8 N, in the case of a powerless actuating unit 13 of the actuator unit 15, a force F_(fed) of the compression spring 43 of 1.14 N is required to release the clamped assembly 39 and restore the actuator unit 15.

LIST OF DESIGNATIONS

1 Coolant pump

2 Internal combustion engine

3 Traction mechanism drive

4 Traction mechanism

5 Pulley wheel

6 Pulley wheel

7 Cooling circuit

8 Hydraulic circuit

10 Actuator system

11 Radial piston pump

12 Linear freewheel

13 Actuating element

15 Actuator unit

18 Pump housing

19 Impeller wheel

20 Pump shaft

21 Antifriction bearing

22 Suction connection

23 Spiral channel

24 Pump cover

25 Guide plate

26 Outflow region

27 Rear wall

28 Push rod

29 Intake piston

30 Counterpiston

31 Through hole

32 Control element

33 Inner contour

34 Cutout

35 Rotational axis

36 Rotational axis

37 Spring element

38 Seal

39 Clamped assembly

40 Clamping body

41 Guide sleeve

42 Clamping cone

43 Compression spring

46 Intake valve

47 Push-out opening

48 One-way valve

49 Pressure space

50 Longitudinal bore

51 Closing valve

52 High pressure space

54 Actuating piston

56 Failsafe device

E Eccentricity

F_(fed) Spring force

F_(exz) Eccentric force

N Perpendicular force

R Frictional force

A Wedge angle

μ Coefficient of friction 

1. A coolant pump of an internal combustion engine, comprising a pump housing in which a pump shaft is mounted rotatably, the pump shaft is configured as a hollow shaft and has an associated impeller wheel connected on one end thereof which delivers a coolant as volumetric flow via a suction connection into a spiral channel, a guide plate on the impeller wheel to adjust a volumetric flow that is axially displaceable between two end positions in an infinitely variable manner and is connected in a rotationally rigid manner to a push rod that is guided in the pump shaft and is connected to an actuator system, the actuator system comprises a radial piston pump which is integrated within the coolant pump and includes a main or intake piston and a counterpiston, which are guided in a through hole of the pump shaft, and are inserted so as to lie opposite one another, to delimit a pressure space, and are enclosed on an outside by a radially or linearly displaceable control element which is guided in a cutout in the pump housing, an adjustment of which takes place via an actuator unit which includes an electrically operated actuating element and a linear freewheel.
 2. The coolant pump as claimed in claim 1, wherein a clamped assembly of the linear freewheel of the actuator unit, which makes a self-locking action possible, comprises at least two clamping bodies which are inserted in a guide sleeve, are guided on an outside on a cutout of the pump housing and on an inside enclose a clamping cone which is assigned to the control element.
 3. The coolant pump as claimed in claim 2, wherein the clamping cone which tapers in a direction of the guide sleeve engages in regions into the guide sleeve and is enclosed by a compression spring which is inserted between the control element and the guide sleeve.
 4. The coolant pump as claimed in claim 3, wherein, for a powerless actuating element, the compression spring exerts an axial force which releases the clamped assembly of the linear freewheel and moves it into an initial position or a neutral position.
 5. The coolant pump as claimed in claim 1, wherein an electromagnet is provided as the actuating element for the actuator unit.
 6. The coolant pump as claimed in claim 1, wherein the actuator unit provides a range of force of ≧10 N for the actuating element, the compression spring has a range of force of from ≧1.2 N to ≦3 N, and the linear freewheel has a wedge angle α of ≦5.7° with a coefficient of friction μ of 0.1 in order to achieve a self-locking action.
 7. The coolant pump as claimed in claim 1, wherein an eccentricity (E) of the main piston and counterpiston which are offset by 180° with respect to one another and are guided on an inner contour of the control element can be influenced by the control element which is inserted in the pump housing such that it is sealed, fixed rotationally and displaceable radially in an infinitely variable manner.
 8. The coolant pump as claimed in claim 1, wherein a spring element is inserted between the main piston and the counterpiston of the radial piston pump, and the main piston includes an intake channel or an intake valve for entry of hydraulic fluid, and the hydraulic fluid exits into the pressure space via a one-way valve.
 9. The coolant pump as claimed in claim 8, wherein, in the actuation phase, a partial quantity of the hydraulic fluid is displaced, in the case of a pressure gradient, out of the pressure space via a closing valve of the pump shaft into a high pressure space, in which an actuating piston which is coupled to the push rod of the guide plate is loaded.
 10. The coolant pump as claimed in claim 1, wherein, as a failure safeguard for the actuator system, the push rod interacts with a failsafe device which comprises a spring element. 